Ion channels are proteins that span the lipid bilayer of the cell membrane and provide an aqueous pathway through which specific ions such as Na+, K+, Ca2+ and Cl− can pass (Herbert, 1998). Potassium channels represent the largest and most diverse sub-group of ion channels and they play a central role in regulating the membrane potential and controlling cellular excitability (Armstrong & Hille, 1998). Potassium channels have been categorized into gene families based on their amino acid sequence and their biophysical properties (for nomenclature see Gutman et al., 2003).
Compounds which modulate potassium channels have multiple therapeutic applications in several disease areas including cardiovascular, neuronal, auditory, renal, metabolic and cell proliferation (Shieh et al., 2000; Ford et al., 2002). More specifically potassium channels such as Kv4.3, Kir2.1, hERG, KCNQ1/minK, and Kv1.5 are involved in the repolarisation phase of the action potential in cardiac myocytes. These potassium channels subtypes have been associated with cardiovascular diseases and disorders including long QT syndrome, hypertrophy, ventricular fibrillation, and atrial fibrillation, all of which can cause cardiac failure and fatality (Marban, 2002).
The human delayed rectifier voltage gated potassium channel subunit, Kv1.5, is exclusively expressed in atrial myocytes and is believed to offer therapeutic opportunities for the management of atrial fibrillation for several different reasons (see review of Brendel and Peukert, 2002): (i) There is evidence that Kv1.5 underlies the cardiac ultrarapid delayed rectifier (Kv(ur)) physiological current in humans due to similar biophysical and pharmacological properties (Wang et al., 1993; and Fedida et al., 1993). This has been supported with antisense oligonucleotides to Kv1.5 which have been shown to reduce Kv(ur) amplitude in human atrial myocytes (Feng et al., 1997). (ii) electrophysiological recordings have demonstrated that Kv(ur) is selectively expressed in atrial myocytes, and therefore avoids inducing potentially fatal ventricular arrhythmia through interfering with ventricular repolarisation (Amos et al., 1996; Li et al., 1996; and Nattel, 2002). (iii) Inhibiting Kv(ur) in atrial fibrillation-type human atrial myocytes prolonged the action potential duration compared to normal healthy human atrial myocytes (Courtemanche et al., 1999). (iv) Prolonging the action potential duration by selectively inhibiting Kv1.5 could present safer pharmacological interventions for protecting against atrial re-entrant arrhythmias such as atrial fibrillation and atrial flutter compared to traditional class III antiarrythmics, by prolonging the atrial refractory period while leaving ventricular refractoriness unaltered (Nattel et al., 1999, Knobloch et al., 2002; and Wirth et al., 2003). Class III antiarrythmics have been widely reported as a preferred method for treating cardiac arrhythmias (Colatsky et al., 1990).
Traditional and novel class III antiarrythmic potassium channel blockers have been reported to have a mechanism of action by directly modulating Kv1.5 or Kv(ur). The known class III antiarrythmics ambasilide (Feng et al., 1997), quinidine (Wang et al., 1995), clofilium (Malayev et al., 1995) and bertosamil (Godreau et al., 2002) have all been reported as potassium channel blockers of Kv(ur) in human atrial myocytes. The novel benzopyran derivative, NIP-142, blocks Kv1.5 channels, prolongs the atrial refractory period and terminates atrial fibrillation and flutter in in vivo canine models (Matsuda et al., 2001), and 59947 inhibited Kv1.5 stably expressed in both Xenopus oocytes and Chinese hamster ovary (CHO) cells and Kv(ur) in native rat and human cardiac myocytes (Bachmann et al., 2001). Elsewhere, other novel potassium channel modulators which target Kv1.5 or Kv(ur) have been described for the treatment of cardiac arrhythmias, these include biphenyls (Peukert et al 2003), thiophene carboxylic acid amides (WO0248131), bisaryl derivatives (WO0244137, WO0246162), carbonamide derivatives (WO0100573, WO0125189) anthranillic acid amides (WO2002100825, WO02088073, WO02087568), dihydropyrimidines (WO0140231), cycloakyl derivatives (WO03063797), indane derivatives (WO0146155 WO9804521), tetralin benzocycloheptane derivatives (WO9937607), thiazolindone and metathiazanone derivatives (WO9962891), benzamide derivatives (WO0025774), isoquinoline derivatives (WO0224655), pyridazinones derivatives (WO9818475 WO9818476), chroman derivatives (WO9804542), benzopyran derivatives (WO0121610, WO03000675, WO0121609, WO0125224, WO02064581), benzoxazine derivatives (WO0012492), and the novel compound A1998 purified from Ocean material (Xu & Xu, 2000). General voltage gated potassium channel inhibitors have been reported which could also modulate Kv1.5 (U.S. Ser. No. 05/753,676, U.S. Ser. No. 05/821,251, EP0743936B).
Thienopyrimidines have been reported to be useful as anti-inflammatory, anti-fungal, anti-osteoporosis and anti-microbial agents, and as cardiovascular agents (acting through modulation of the phosphodiesterase group of enzymes or through modulation of the sodium/proton exchange system) amongst others.
Thieno[2,3-d]-pyrimidines substituted in the 4-position with an optionally substituted benzylamine or phenethylamine moiety and in the 5-position with a methyl group may serve as anti-inflammatory or anti-osteoporosis agents (Katada et al., 1999). Such compounds were shown to modulate the activity of several cell types including leukocytes, which originate from hematopoietic precursor cells in the bone marrow. Increased activity in leukocytes can lead to various inflammatory diseases; therefore compounds cytotoxic to leukocytes could function as anti-inflammatory drugs. Such compounds are thought to suppress cellular activity by binding to integrins on the surface of leukocytes and preventing downstream cellular signalling events. Thieno[2,3-d]pyrimidines substituted in the 4-position with heteroarylthiols, aryl thiols, arylmethyl thiols, heteroarylamines, benzylamine, hydroxyl and chloro groups may also be useful anti-inflammatory agents (Stewart et al., 2001). This series of compounds were shown to inhibit induced expression of cell adhesion molecules on the luminal surface of vascular endothelial thus preventing the adhesion of leukocytes at the site of inflammation.
Thieno[2,3-d]pyrimidines with a substituted hydrazine in the 4-position and a phenyl group in the 5 position (Hozien et al., 1996), tetrahydrobenzo[b]thieno[2,3-d]pyrimidines (Ismail et al., 1995), thieno[2,3-d]pyrimidines which have a hydrogen, chloro, hydrazine, heterocyclyl, amino, methyl, ethyl or phenyl group in the 2-position, an alkylamino, alkylarylamino, amino, dialkylamino or hydrazino substituent in the 4-position, a hydrogen or methyl group in the 5-position, a hydrogen, methyl acetamide or phenyl group in the 6-position or a tetramethylene in the 5,6-position (GB7549025), and the lead series of 5-phenyl- and 5,6-tetramethylenethieno[2,3-d]pyrimidines with methyl or phenyl in the 2-position and alkylamino or arylamino in the 4-position (Konno et al., 1989) have all been shown to have anti-microbial activity. Tetrahydrobenzothieno[2,3-d]pyrimidine with the 2-oxo-3-pyrrolidinylmethylene-hydrazino moiety in the 4-position showed some herbicidal activity against velvet leaf (Ram et al., 1981). It has also been reported that 4-chlorotetrahydrobenzothieno[2,3-d]pyrimidine is herbicidal, tetrahydrobenzothieno[2,3-d]pyrimidines with a thiol, hydrazine, 2-fluoroanilino, 3-fluoroanilino or 4-diethylanilino substituent in the 4-position are bactericidal against Streptococcus fecales and tetrahyrobenzothieno[2,3-d]pyrimidines with a 2,4-dichlorobenzylamino or 2-fluoroanilino substituent in the 4-position are fungicidal against Pythium (Ram, 1979). Thieno[2,3-d]pyrimidines with a hydrogen, hydroxyl, thiol, halogen or cyano group in the 2-position, alkylamino, arylalkylamino or hydroxyalkyl amino groups in the 4-position, a hydrogen, alkyl or halogen in the 5- and/or 6-position or alkylene in the 5,6-position have been reported as tick-control agents (AU 521790).
Elsewhere, tetrahydrobenzo[b]thieno[2,3-d]pyrimidines exhibited anti-tumour activity (Shehata et al., 1996) and analgesic activity half that of aspirin (Moneer et al., 1994), a series of thieno[2,3-d]pyrimidines with 4-alkylamino or arylamino, 5-H or 5-methyl, 6-methyl or 5,6-tetramethylene were shown to have potential as anticytokinins (Jordis et al., 1986), a series of 5,6-dimethyl-thieno[2,3-d]pyrimidines and 5,6-tetramethylenethieno[2,3-d]pyrimidines, both substituted in the 2-position with arylamines or heterocyclic amines and in the 4-position with arylamines displayed blood platelet aggregation inhibiting properties (DD 226893), pyrano- and thiopyrano[3,4-b]thieno[5,4-d]pyrimidines with the 4-position substituted with amino, butylamine, aniline, cyclohexylamine, benzylamine, phenethylamine and 2-hydroxyethylamine have been reported to exhibit anticonvulsive activity (Noravyan et al., 1977), and 4-[(Benzo-2,1,3-thiadiazolyl-4)amino]-5,6,7,8-tetrahydrobenzothieno-(2,3-d)-pyrimidine has been reported to possess anthelmintic activity in larval alveolar echinococcosis (RU 2116309).
Thieno[2,3-d]pyrimidines with a substituted amino group at the 4-position, hydrogen, alkyl or halo substitution at the 5 and 6-positions and an alkyl chain at the 2-position are claimed to be inhibitors of phosphodiesterase V and useful in the treatment of cardiovascular diseases and for disturbances in potency (DE10104802).
Elsewhere, 5-alkyl thieno[2,3-d]pyrimidines with a piperazinyl substituent at the 4-position were found to be inhibitors of the sodium/proton exchanger and useful in the treatment of various cardiovascular disorders, including angina pectoris and arrhythmia (WO 01/27107).
4-[(phenyl)amino]-thieno[2,3-d]pyrimidines bearing a 5-thiophenyl substituent and a 2-methyl substituent were found to have molluscicidal activity (Hosni et al, Acta Poloniae Pharmaceutica, 1999, 56(1), 49-56).
Recently thienopyrimidines have also been reported as potent VEGFR inhibitors (Munchhof, 2004).
Several publications disclose compounds which are indicated as acting on potassium channels. Thus, U.S. Pat. No. 6,531,495 discloses 2′-aminomethylbiphenyl-2-carboxamides, WO2002/100825 discloses anthranillic acid amides as antiarrhythmics and WO2002/036556 discloses acylaminoalkylbenzenesulfonamides as cardiovascular agents.
Thienopyrimidine compounds that are useful as potassium channel inhibitors, particularly for inhibiting potassium channels Kv1.5 or Kv(ur), are reported in WO 2004/111057.